<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      let sum = 0
      function changeNum(x, y) {
        sum = x
        x = y
        y = sum

        document.write(`第一个值是 ${x},第二个值是 ${y}  `)
      }

      changeNum(1, 2)
      changeNum('red', 'yellow')
      changeNum('green', 'blue')
    </script>
  </body>
</html>
